Alkaline zinc plating baths



Patented June 8, 1954 U NITED S PATE-N T OFFICE ZINC PLTING BATHS MyronB. Diggin, .Matawan, land Otto Kardos,

Keypor't, N. J., .assignors to Hanson-Van Winkle-Munning Company, Matawan,N. 'J a' coi'- poration of 'New Jersey No Drawing.' 4Application August 37, :1951, Serialy No. 240,280

3 Claims. l

This invention relates to `itl-re -eleotrodepo'sition of lzinc from alkali cyanide baths, and v-rnore par#- ticularly to a new type ci addition agent iersuch baths We have found that certain bath-'solubleft'son- 'densation polymers prepared from :an aliphatic alkylenepolyarnine (such as ethylenediaininefprepylenediamine and higher member-s of lthis l'series; diethylenetriamina triethyl'enetetramine, `tetraethylenepentamine and so on; dipropylene- Vtrianiine; N-hydroxyethyl /ethylenediamine LNNJ- ldihydroxyethyi yethylenediaminey Lediamino'- prepa-no1) asonereactant, and furfural, turtura'l sodium bisulphite, formaldehyde, and/or iormaldehyde sodium bisulphite'as the other reactants exert a strong brightening-action on Athe electrodeposits, vwhen added vin relatively `'small amounts to a cyanide zinc rplating bath,

The vcomposition of 4the yaqueous plating solutions used in our experiments was:

y(ra/gal. Zinc cyanide .f8 :to 12 Sodium cyanide A to 9 :Sodiumhydroxide -8 to 12 Before use, 'the solutions Weretreatedwith'z'inc dust to eliminate metallic impurities. Gur eirperiments were performed at room temperature.

The usual bright dips-can-beappli'edto the zinc plates obtained, but `in many 'cases this is not necessary.

'l `mol. diethylenetriamine reacted With 1 mol. furfural .gave products of ylittle brightening elln ciency; with Zmols. furfural, products of higher We vobtained considerably better addition.

agents by .using the furfural-sodium bisulphite addition'cornpound instead of furiural 'itself Also partial or entire lsubstitution of N-hydroxyethyl ethylene'diamine, NN'-dihydroxyethyl ethylenediamine or 1,3-diarnino-2 propanol for diethylenetriainine (or triethylenetetramine) gavefimproved `results.

Example 1 To 103.2 g. (1 mol.) diethylenetriamine, 96.1 g. (1 mol.) furiural were added under stirring, and

2 the reactionprodiiot wasmeatedto '110 C. Then, after cooling .to -roo'x'n temperature, 21'6 g. (2166 inls.) "formaldehyde '(37%) were added andthe reaction product heated 'for l0 minutes .in a Water 'b'a'th to 90 C. The n'al .product was diluted ltO l '.liter. A cyanide Zinc -plating bath containing per .liter l0 to 25 nil. o'i this b'rightener .solution gave ilarg'e Iarle'as o'f brilliandy 'in the Hull dell, ythe optimum df 'brilliancy occurring at higher current densities with increasing brightener concentration.

Lower and higher amounts of formaldehyde than those indicated above gave less potent brigh'ten'ers. "Tco .lon-g. and :too lhigh heating of these condensation :products iincreased Atheir brightenin'g .efficiency ibut provoked :blistering of the electrodeposits over a steel hase.

Example The reaction product was Vthen'heated for a short .time to C., cooled, and 12156 rg. (125 -molsD lformaldehyde (37%) Werel added under stirring :and the product :again shortly heated to 85 C.

.This dark brown lsyr'upy reactionproduct wla's 'diluted with Water to make 1 liter; 20 to $0 .m1, .oflthis solution, When addedrto 1 liter rzinc bath, .produced bright zinc deposits over a Wide current vdensity Irange.

Example 3 .26 g. 6.0.25 mol.) ,hydroxyethy iethylenedia- :minewand 1g.y (0:5 rmol.) furural-sodium bisulphite (powdered) were mixed. Strong heat levolution occurred-anda dark -broW-n zfresin .resulted which wa-sidissolyed iin water to make .250 ml. 24 -ml.:of this isolation; when-added to f1 liter zinc ybath, .fgave :brilliant electrodcpo'sits 'in fthe high 'current dens-ity range.

Example 4 To 36.6 g. (0;2'5nroli) `triethylen'etetranrimewere added 'under :stirring i2() sg. A(025 incl.) formaldefhyde and :then 100 vvag. (0.15 :molo cnrfuralesodiinn 'bisulphite 'The :reaction product .was heated to around C., where-.gasevoluticn volume .increase occurred. 'Therresulting :dark acolored resin was dissolved -to 250 -rl. Only 5I xml. idf this .so'lu-tioli,` when added fto'l 'liter .zinc .-b'atlli, caused the ormati'nofbrilliant but 1pitted electrodeposits.

When the reaction product was heated only to '70 C. and dissolved to 250 ml., larger brightener additions Were required (14 mL/Iiter), but

pit-free bright zinc deposits were obtained over a Wide current density range (approximately 20 to 50 amps/sqft.) in the Hull cell.

Examples 5 to 19 A great number of reaction products of triethylenetetramine, alone or mixed with N-hydroxyethyl ethylenediamine (or sometimes with NN-dihydroxyethyl ethylenediamine), with furfural-sodium bisulphite (concentrated aqueous solution) and formaldehyde were prepared. The addition agents prepared from triethylenetetramine gave somewhat better results than those prepared from diethylenetriamine or tetraethylenepentamine.

The following table gives the concentration of the reactants in mols. The procedure was as follows:

To the polyamine or the polyamine mixture, aqueous formaldehyde (37%) (if indicated in the table) was slowly added under stirring and cooling. Then a solution of 1 mol. furfural and 1 mol. sodium bisulphite (0.5 mol. sodium metabisulphite) in 200 ml. of water, aged for at least half an hour, was added under stirring and, if required, cooling. Then the nal formaldehyde (if indicated in the table) was added and the reaction product heated for about 15 minutes at slight boiling. When larger quantities were prepared, external heating was not necessary as the reactions are strongly exothermic.

1st or 2nd N-Hy- 2nd or 3rd E Triethyldroxytlilx Resgon Reaction xample enetetraethyl eth- Formal. FmfuraL Step.

mme yl'lga' dehyde sodium lolrlml' bisuiphite e y e l. (l 1. (l 2.0 1.0 2. 2.0 l. 0 0. 5 1. 0 2. 0 1. 0 0. 5 2.0 2. 0 1.() 1. 0 2.0 1. 0 0. 5 0. 5 1.0 2.0 0. 5 0.5 0. 5 2. 1. 0 0. 5 O. 5 1.0 2.0 l. 0 (l. 5 0. 5 2. 0 0. 5 0. 5 2. 0 1. 0 0. 5 0. 5 2. U 2.0 0. 5 0. 5 l. 0 l. 33 0. 5 0. 5 l. 0 2. 66 0. 5 (l. 5 0. 5 2. 0 O. 25 0.75 1. 0 2. 0

Above reaction products were diluted to 1 liter, and to 15 ml. or" these solutions, equivalent to about 2.5 to 9.5 grams of reaction products, were added to 1 liter plating bath. They all exert a strong brightening action over a wide current density range (approximately 10 to 50 amps./sq. it). Brighteners #10 and #14 seemed to be the best suitable for still zinc plating. .Brighteners and #19 were less good than the average.

These addition agents were very stable in the aqueous stock solution, but less so in the zinc plating bath, to which they have to be added periodically in order to maintain a high degree of brightness of the electrodeposits.

However, all these addition agents of high brightening power have a tendency to produce blistering of the zinc deposit on steel in the low current density range, if the plating time is about 10 to 15 minutes and the plated parts are soaked in almost boiling water. This blistering tendency is especially pronounced in older baths replenished several times with brightener.

We have discovered the surprising fact that adpolymer dition of very small amounts of the higher molecular polyamines suppresses this tendency to blistering. This anti-blistering action increases with increasing molecular weight of the polyamine. Thus a polyethylene polyamine of an average molecular weight of 65D is more effective than tetraethylenepentamine, and the latter more than triethylenetetramine. The very small amount of 0.1 g./liter of said polyethylene polyamine was sumcient to suppress this blistering tendency. However, an excess of these higher polyamines reduces the brightness of the electrodeposits considerably.

Complete elimination of this blistering tendency was also obtained by introducing formaldehyde-sodium bisulphite in the brightener molecule.

Eample 20 To a mixture of triethylenetetramine 366 g. (2.5 mols.) and N-hydroxyethyl ethylenediamine 260 g. (2.5 mols.) were slowly added, with stirring, formaldehyde (37%) 375 m1. (approximately 5 mols.). Then an aldehyde-sodium bisulphite solution was prepared as follows: To 2300 ml. of Water were added 375 ml. formaldehyde (5 mols.) then, with stirring, 1500 g. of sodium inetabisulphite (corresponding to 15 mois. sodium bisulphite) and linally 961 g. furfural (10 mola).

After about half an hour of aging, this mixed aldehyde-bisulphite solution was added to the polyamine-formaldehyde reaction product with stirring and the nal mixture heated to boiling, where it was kept for about 10 minutes.

The reaction product was finally diluted to 5 liters. On addition of 10 nil/liter of this brightener stock solution, equivalent to about 6.5 g./liter of reaction product to a standard zinc bath, uniform bright and blister-free zinc electrodeposits were obtained over a wide current density range (20 to 70 and more amps/sq. it.) and the bath could be easily maintained in good performance by periodic additions of brightener.

We claim:

1. An aqueous alkaline cyanide zinc plating bath containing, in amounts of substantially 2.5 to 9.5 g./liter, as a brightening agent a condensation polymer of an aliphatic alkylenepolyamine with furfural-sodium bisulphite and formaldehyde, 0 to 50% of the latter in the form of its sodium bisulphite compounds.

2. An aqueous alkaline cyanide zinc plating bath containing, in amounts of substantially 6-.5 g./liter, as a brightening agent a condensation of triethylenetetramme, N-hydroxyethyl ethylenediamine, formaldehyde, ururalsodium bisulphite and formaldehyde-sodium bisulphite.

3. An aqueous alkaline cyanide zinc plating bath containing, in amounts of substantially 6.5 g./liter, as a brightening agent a condensation polymer of 1 mol. triethylenetetramine, 1 mol. N-hydroxyethyl ethylenediamine, 2 mols. formaldehyde, 4 niels. furfural-sodium bisulphite and 2 mois. formaldehyde-sodium bisulphite.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,384,395 Harford Sept. 4, 1945 2,495,629 Chester et al. Jan. 24, 1950 2,589,209 Kardos Mar. 18, 1952 

1. AN AQUEOUS AKALINE CYANIDE ZINC PLATING BATH CONTAINING, IN AMOUNTS OF SUBSTANTIALLY 2.5 TO 9.5 G./LITER, AS A BRIGHTENING AGENT A CONDENSATION POLYMER OF AN ALIPHATIC ALKYLENEPOLYAMINE WITH FURFURAL-SODIUM BISULPHITE AND FORMALDEHYDE, 0 TO 50% OF THE LATTER IN THE FORM OF ITS SODIUM BISULPHITE COMPOUNDS. 